This invention relates to a Stirling engine, and in particular it relates to a Stirling engine in which lubricating oil can be prevented from reaching the piston and entering the heat exchanger of the engine.
FIG. 1 is a cross-sectional view of a conventional, single-cylinder Stirling engine such as that described by G. Walker in the book "Stirling Engine" (Oxford University Press, 1980). In the figure, element number 1 is a crankcase which serves as a base for the engine. Element number 2 is a flange which is secured to the crankcase 1 by bolts or other suitable fasteners which pass through holes formed in the crankcase 1, and element number 3 is a bearing housing which is secured to the crankcase 1 in the same manner as the flange 2. Element number 4 is a flange which is secured to the crankcase 1, element number 5 is a bearing which is secured to the bearing housing 3, element number 6 is a bearing which is secured to the flange 2, and element number 7 is a crankshaft which is rotatably supported by bearing 5 and bearing 6 and which transmits the power generated by the Stirling engine to an unillustrated load. Element number 8 is a mechanical seal which surrounds the crankshaft 7 and prevents gas from leaking from the inside of the crankcase 1. Element number 9 and element number 10 are balance weights which are secured to the crankshaft 7 and which balance it during rotation. Elements number 11 and 12 are piston connecting rods which are rotatably connected to the crankshaft 7 by unillustrated bearings. The upper ends of the piston connecting rods 11 and 12 are connected to a cylindrical crosshead 13, and the crosshead 13 is in turn rigidly connected to a piston 15 by a hollow piston rod 14. The crosshead 13 and the piston 15 are slidably disposed inside a cylinder 16 which is rigidly secured to the upper portion of the crankcase 1. Element number 24 is an annular airproof wall which is secured to the inner surface of the cylinder 16. Its inner surface surrounds the outer surface of the piston rod 14, and an unillustrated seal is provided between the airproof wall 24 and the piston rod 14. The airproof wall 24 prevents the spread of lubricating oil from the crosshead side to the piston side as well as the inflow of gas. Element number 25 is a compression buffer space with a relatively large volume which absorbs variations in pressure which develop in the space between the piston 15 and the airproof wall 24 during operation of the engine. Element number 19 is a first displacer connecting rod which is rotatably connected to the crankshaft 7 by an unillustrated bearing. Element number 20 is a pin and element number 21 is a second displacer connecting rod which is connected to the first displacer connecting rod 19 by the pin 20. The second displacer connecting rod 21 passes through the center of the crosshead 13, the piston rod 14, and the piston 15, and is secured to a displacer 22 which is slidably disposed inside the upper portion of the cylinder 16. The bottom of the crankcase 1 is filled with lubricating oil 23 for lubricating the moving portions of the engine.
During the operation of a conventional Stirling engine of this type, the outer surface of the crosshead 13 and the inner surface of the cylinder 16 are lubricated by the oil 23. The reciprocating motion of the crosshead 13 forms the oil 23 into a mist which is scattered into the space between the crosshead 13 and the piston 15. This mist of lubricating oil 23 adheres to the piston rod 14 and passes through minute gaps between the airproof wall 24 and the piston rod 14 to reach the piston side of the airproof wall 24. This oil 23 may then penetrate into the portion of the cylinder 16 above the piston 15 and enter the unillustrated heat exchanger through the holes 16a in the cylinder, resulting in large decreases in operating efficiency and reliability.